Catheters are used in medical procedures for diagnostic and therapeutic purposes. Diagnostic cardiac catheters are used to infuse radiopaque contrast media into heart blood vessels to allow visualization under fluoroscopy. Therapeutic cardiac balloon catheters are used in angioplasty procedures to dilatate narrowed coronary blood vessels. Guide catheters are often used as conduits, to guide diagnostic and therapeutic catheters to a target position in a vessel.
Cardiac catheters are often inserted through an incision in the femoral artery near the groin, advanced through the femoral artery, advanced over the aortic arch, and inserted into a coronary artery ostium. Once the catheter distal tip is within the ostium, it can be further advanced into smaller branch arteries, until the target site in a coronary artery is reached.
Advancing a catheter along the above described path requires pushability, torqueability and flexibility in differing degrees in different regions of the catheter shaft. In particular, the proximal region of the catheter shaft will ultimately lie within the femoral artery, where flexibility is not as important as the pushability and torqueability required to maneuver the more distal regions of the catheter disposed within the coronary arteries. The intermediate regions between the proximal and distal regions may be required to bend over the aortic arch, where some greater degree of flexibility is required. The distal region of the catheter requires a high degree of flexibility to maneuver through the tortuous path through curved and ever smaller branch arteries.
The intermediate region thus requires more flexibility than the proximal region, and the distal region requires more flexibility than the intermediate region. This increasing flexibility has been provided for in catheters by making different catheter regions from tubular materials having different flexibilities. Individual tubes of appropriate length are joined at their respective ends to form a longer tube having the different flexibility regions. A more rigid tube may be joined at its distal end to a more flexible tube. Where the tubes are joined, there is a discontinuity or sudden change in flexibility. A gradual change in flexibility would be preferable as being less prone to kinking and better matched to the gradual increased need for flexibility over the catheter length.
What has not been heretofore provided and what would be desirable is a catheter tube having improved, gradually distally increasing flexibility. What would be desirable is a catheter tube having controlled flexibility increases over a substantial length of the catheter.